Submerged smelting

ABSTRACT

Smelting of mineral products such as concentrates, rich ores and calcines in which the copper plus zinc content comprises a substantial value is effected by injecting a finely divided mixture of such a mineral product, appropriate fluxes, a fuel (preferably solid) and an oxygen bearing gas into a bath of molten slag. The copper when present forms droplets of matte which remain suspended in the turbulent slag until it is removed from the furnace after which it is subsequently settled from the slag. Another component is vaporized and subsequently recovered; this may be zinc metal, volatile sulfides or sulfur either as the element or its compounds, depending on the composition of the material being treated.

United States Patent Quarm July 1, 1975 SUBMERGED SMELTING 3,27l,l34 9/1966 Derham I 75/87 328L236 I0 1966 M 75 73 [75] Inventor: Thomas A. A. Quarm, Lafayette, elssner I Primary Examiner-P. D Rosenberg [73] Assignee: Bechtel International Corporation,

San Francisco, Calif. [57 ABSTRACT [22] Filed: Jan. 5,1973 Smelting of mineral products such as concentrates,

Appl. No.: 321,220

Related U.S. Application Data [63] Continuation-impart of Ser. No. 858,997, Septv 18,

I969, abandoned.

[52] US. Cl. 75/21; 75/72, 75/87 [51] Int. Cl. C22b 15/00; C22b 19/20 [58] Field of Search 75/72-79, 87, 75/88, 21

[56] References Cited UNITED STATES PATENTS 2,685,506 8/1954 Schereschewsky 75/87 rich ores and calcines in which the copper plus zinc content comprises a substantial value is effected by injecting a finely divided mixture of such a mineral product, appropriate fluxes, a fuel (preferably solid) and an oxygen bearing gas into a bath of molten slag. The copper when present forms droplets of matte which remain suspended in the turbulent slag until it is removed from the furnace after which it is subsequently settled from the slag. Another component is vaporized and subsequently recovered; this may be zinc metal, volatile sulfides or sulfur either as the element or its compounds, depending on the composition of the material being treated.

16 Claims, 8 Drawing Figures COPPER CONC. 400 m;

Cu 28.6% H4 TID Zn 5.2% 2! TF SILICA SAND FLUX I70 TID GAS T0 ACID PLANT SMELTING r FURNACE AIR 5000 saw I COAL 45 TF0 SETTLER I MATT I9 sum 336 rm E 7 w c m; Cu 61.5% IIZTID Zn 6.2% ZI rm COPPER CONC. 450 If!) 1 3 3 53; Iii 1?? 5 34:87: 156T?!) SILICA SAND FLUX 80 T?!) 107W or 5 A5 A 5, 5 C05, ETC. AIIIII 5ETTLER SLAG 260 TH) AIR 5000 56f!!! Cu 0.5% mm] COAL rm I COPPER MATTE I TID IE:- 4 Cu 50% m:

SUBMERGED SMELTING This application is a continuation-in-part of my application Ser. No. 858,997, filed Sept. 18, 1969. and now abandoned.

SUMMARY OF THE INVENTION A simple, low cost smelting process is achieved by continuous injection of a finely divided mineral product such as an ore. concentrate or calcine. along with an appropriate flux, a fuel and an oxygen bearing gas in the correct proportions directly into a bath of molten slag and beneath the upper surface of the slag through submerged tuyeres such as are used in slag-fuming furnaces. The slag acts as a solvent for oxides, as a heattransfer medium, and as an oxygen carrier. The violent agitation caused by injection of the material beneath the slag promotes rapid reaction and permits ready escape of vapors into the bubbles. Passage of bubbles through the slag body provides a scrubbing action to remove dust particles that would otherwise be carried out of the furnace with the gas. The resulting gases and liquids are removed from the furnace and treated further by conventional means to recover the values contained.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. I through 4 each provides a flowsheet illustrating the treatment of various materials in accordance with the present invention.

FIG. 5 is a perspective view ofa standard zinc fuming furnace.

FIG. 6 is a cross section through one of its tuyeres as modified to be used in the furnace of FIG. 7.

FIG. 7 is a fuming furnace modified for trials of submerged smelting in accordance with the examples of this disclosure.

FIGS. 8A through F are cross sections through the various tuyere arrangements to be used in the practice of this invention wherein a. designates means for adding a fluidized fuel,

b. designates means for adding a fluidized metal bearing material and flux, while c. designates a conduit for the main flow of oxygen bearing gas.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following illustrative examples show the application of this invention for smelting of various ores and concentrates.

In these operations, a standard 8 feet X 2i feet slagfuming furnace II, as shown in FIG. 5, was utilized after being modified as shown in FIGS. 6 and 7. The slag utilized to start the test was a dezinced lead slag regularly produced in such a furnace. The furnace was constructed with water jacketed steel plates 2], water being provided in the space between the plates by pipes to and from each plate (not shown). The inner plates of the furnace had a layer of frozen slag on the inner wall of these plates of the order of an inch in thickness. The furnace was connected by a flue 12 to a waste heat boiler and thence to a bag house (not shown) and was regularly used to dezinc batches of lead blast furnace slag. Air is supplied through line 51 while coal fluidized by a minor part of the air is fed through line I5 and nozzle to inside of each of tuyeres l4 and located on oppo- Site sides of the furnace and each tuyere connection has a shut-off valve 19 so that a defective tuyere can be taken out of service.

Referring further to FIG. 5, an opening 20 is provided in one end wall of the furnace to add slag and admit air to burn zinc vapor. In the normal batch operation for zinc fuming, the dezinced slag is removed from the furnace through tap hole 23 into a launder 24 and thence to a settling tank 26 to collect the matte droplets suspended therein. The settled matte, when enough has accumulated, is removed through the tap hole 27 into a launder 28 and thence into a matte ladle 29. The discard slag is removed from the settler 26 through launder 31 and thence into a slag ladle 32.

The furnace of FIG. 5 and half of its tuyeres was modified, as is shown in FIGS. 6 and 7, for injecting fine minerals through alternate tuyeres 14. Each tuyere 14 has a ball valve 17 which can be moved as by a rod (not shown) to permit the tuyere to be cleared of any solids. The valve 19 controlling the supply of coal was turned off at every other tuyere. Through the ball valve 17 of these tuyeres was placed a slip'ftt nozzle 52 which could be removed for punching the tuyere with a rod when necessary. These nozzles were connected by a flexible metal hose 18 to a stainless steel header 47 from a heater 43 fired by burner 44. Mineral materials to be injected were placed in a bin (not shown) having a screw conveyor (not shown) to meter the material into line 42 using a minor part of the air to fluidize and inject the mineral material into the furnace by the heater, header, hose and nozzle.

Injection of mineral into some tuyeres and fuel into the others was an expedient to test my invention, and was successful because the violence of the agitation promptly mixed these ingredients. However, in the practice of my invention, it is preferable to inject both the mineral material and the fuel, each with a minor part of the air, into the major air flow of each tuyere. This is done by making both injections into each tuyere or having one or the other just above or just below each tuyere, as is shown schematically in the several cross section views of FIG. 8.

The fuel regularly used for fuming and used in these tests was pulverized coal having a BTU value of 14,600 per pound and an approximate composition of 72.2% of fixed carbon, 20.3% of volatile material, 3% moisture and 4.5% ash. The ultimate analysis was 84.0% carbon, 4.7% hydrogen, 5.2% oxygen, [2% nitrogen and 0.5% sulfur. Any other solid fuel could be readily used. Liquid and gaseous fuels are less effective when a metal such as zinc is to be reduced to the extent they contain the slow burning short chain saturated hydrocarbons such as methane. Both lime and siliceous fluxes were used for smelting products containing appreciable zinc but smelting copper concentrates needed only a siliceous flux. As it appears diagrammatically in FIG. 6, the fuel air mixture injected through alternate tuyeres directly into the slag burns with a flame, indicated at 33, inside a turbulent pool 34 of the molten slag and below the surface thereof.

EXAMPLE I: ZINC SMELTING An ton lot of zinc calcine was obtained. It was produced by dead roasting a zinc sulfide flotation concentrate. Ten tons of an appropriate ground flux was mixed with it. The mix was placed in the feed bin. When a batch of slag had been dezinced in the furnace, it was not tapped out and the following process was started. The coal was turned off at alternate tuyeres and the mineral injection nozzles were inserted through the ball valves of these tuyeres. The hot calcine-flux mix from heater 43 via line 47 and hoses I8 and the pulverized coal from line were blown with fluidizing air through alternate submerged tuyeres 14 directly into the bath of molten slag of about I200C. With 16,000 SCFM (70F, 14.7 psia) of air total, injection of l l.4 short tons per hour of the calcine-flux mix and 5.8 short tons per hour of coal maintained the bath at about 4% Zn and the temperature of about l200C. The reducing gas and zinc vapor emerging from the bath burnt in the air drawn into the furnace through the charging door 20. The proportion of oxygen used is such that only a minor portion of the carbon in the fuel is oxidized beyond carbon monoxide to form carbon dioxide or else zinc will not be volatilized as metal, but remains in the slag in an oxidized form and sulfide sulfur in the matte is not oxidized beyond Cu S to form copper metal. Gangue and iron in the calcine and the fluxes form a slag similar to that initially present. This was tapped intermittently as required. Copper formed a matte containing a trace of precious metals. This remained suspended in the agitated slag until it was tapped from the furnace via top hole 23. The slag flowed through a settler 26 in which the matte accumulated. After eight hours the lot was smelted, the accumulated matte was tapped into ladle 29, and the furnace was returned to the regular service.

In the practice of my invention, the furnace door must be sealed and the exit 12 instead of going to a waste heat boiler and bag house would, as shown in FIG. 1, go to a condenser to condense the zinc vapor. The gas from the condenser, which will have a calorific value of about 100 BTU/cu. ft., could be used elsewhere where fuel was needed or burned in an ancillary operation for steam and power production. The quantities shown on the flowsheet of FIG. 1 and those which follow come from the examples and are typical but not limiting or restrictive.

The small quantity oflead in the concentrate was also reduced to metal and vaporized. In the practice of my invention. it would be recovered in the condenser with the zinc. The liquid zinc-lead mixture from the condenser could be separated to obtain Prime Western grade zinc or could be purified further by refluxing.

In the practice of my invention, the slag composition is not criticalv I prefer that slag which can be formed with the least expense for fluxes and which is fluid enough at about l200C. for matte to settle reasonably rapidly and completely after the slag is tapped from the turbulent furnace into the settler.

A zinc concentrate of this type can conventionally be roasted and then subjected to leaching and electrolysis. The power consumption. after crediting the steam from waste heat recovery, is equivalent to about 27,000 BTU per pound of zinc. The process of this invention. as shown in FIG. I. consumed only l4,000 BTU per pound of zinc without credit for the steam from waste heat recovery or the fuel value of the condenser gas. About 5,000 BTU per pound of zinc must be debited. however, for refining by refluxing.

EXAMPLE 2: ZINC-COPPER CALCINE A 267 ton lot of zinc-copper concentrate was given a partial roast in a fluid bed reactor. To the 220 tons of calcine containing 6% sulfide sulfur was added 79 tons of appropriate fluxes. This mix was then smelted in the same manner as the zinc-calcine mix of Example 1. This time, with 16000 SCFM of air total, feeding 18.7 tons per hour of mix and 5.3 tons per hour of coal maintained the slag bath temperature and composition at steady values. Slag with matte in suspension was tapped from the furnace at intervals and separated in a settler. This run was stopped after eight hours when half the calcine mix had been used and the furnace was then returned to regular service.

In the practice of my invention on this material, the furnace door 20 would be closed and a condenser would replace the boiler and bag house beyond exit 12. The flowsheet is given in FIG. 2.

EXAMPLE 3: ZINC-COPPER CALCINE WITH OXYGEN ENRICHMENT A trailer of liquid oxygen was connected to a vaporizer through meters and to the blower so that its output to the smelting furnace would contain 26% oxygen. The remaining half of the mix of Example 2 was smelted.

It was now found with 16,000 SCFM of enriched air, 28 tons per hour of mix and 6.9 tons per hour of coal held the bath temperature and zinc content steady. The test was stopped in 5 hours and 20 minutes when the feed was exhausted.

This practice of the invention is also illustrated in FIG. 2 by the figures in parentheses.

EXAMPLE 4: COPPER SMELTING WITH ACID PRODUCTION A I00 ton lot of copper concentrate was mixed with 42.5 tons of silica sand flux and smelted in the fuming furnace as in the previous example. It was desired to use the sulfur in the concentrate in excess of that needed to form matte as fuel and to volatilize it as $0 With 16,000 SCFM of air, 23.8 tons per hour of the mix was smelted while only 1.87 tons per hour of coal was required to hold temperature at l200C. Slag with matte in suspension was tapped at intervals and separated in a settler. After six hours, the feed was exhausted and the run was stopped. The practice of submerged smelting of copper concentrates is illustrated in FIG. 3.

The furnace door 20 used in the practice of this embodiment, unlike those used in the practice taught in the preceding examples. need not be closed. Inflow of air to provide oxygen equal to half the volume of SO produced is needed for acid manufacture. This air can be drawn in through furnace door 20 or added after the waste heat boiler. or after gas cleaning or divided among these addition points. Oxygen supplied through the tuyeres must be limited so that the copper matte is not oxidized beyond Cu S to form metallic copper which. on account of its high density, despite the turbulence. might accumulate as a layer at the bottom of the furnace. Such a layer of metallic copper would displace the frozen slag which insulates the water cooled metal plates and destroy the furnace. Such a copper layer is sought by Worner in US. Pat. No. 3,437,472, by Themelis et al. in US. Pat. No. 3,437,475 and by lv lissner in US. Pat. No. 3,281,236. These and other processes aimed at the continuous production of blister copper can only be practiced in refractory lined furnaces. The S0; bearing gasses from exit 12, with or without a waste heat boiler, would be cleaned of any particulates. The S: contained then could be converted into acid, recovered as a liquid or reduced to sulfur as desired. With oxygen enrichment, the need for coal can be reduced further or eliminated.

The zinc in the concentrate dissolved in the stag and was recovered subsequently by slag-fuming. This concentrate also contained 0.2% Pb; analysis of matte and slag showed only traces. This shows the lead was volatilized, presumably as the sulfide or oxide.

In contrast to conventional copper smelting, violent agitation in submerged smelting promotes reaction between magnetite and sulfide so that the tapped slag has minimal magnetite and hence many of the usual magnetite problems are avoided. A reverberatory furnace without partial roasting smelts about 0.25 ton of charge per square foot per day whereas submerged smelting (not counting the settler) smelts 2.4 tons per square foot per day. A reverberatory furnace would require to 6 X [0' BTU per ton of concentrate smelted, whereas submerged smelting consumes only 3.3 X if) BTU.

EXAMPLE 5: COPPER MATTE SMELTING WITH SULFUR PRODUCTION A 100 ton lot of chalcopyrite concentrate which analyzed: Cu 20.3%, Fe 35.8%, S 35.8%, SiO 2.0% was mixed with [8 tons of silica sand and smelted as in Example 4, but with more fuel so less sulfur was oxidized.

With 16,000 SCFM of air and 22 tons per hour of the mixture being fed directly into the slag, when the coal rate was increased to 3.33 tons per hour, the bath temperature held steady at l200C. A probe was inserted to sample the gases leaving the bath before they had a chance to burn. Gas samples were obtained having less than 0.2% $0 by volume. Some elemental sulfur was observed in the condenser and the odor of H S was noted at the sampling ejector. After 5 hours and 22 minutes the feed was exhausted and the run was stopped. The quantities and flowsheet are given in FIG. 4.

This example shows that in the submerged smelting of copper ores, increasing the coal restricts the oxygen available to oxidize sulfide sulfur so that the sulfur present in excess of that needed to form CU S is largely not oxidized beyond the elemental state. Under these conditions no copper metal can form. At the same time, the slag acting as an oxygen carrier attaches the iron sulfides to form FeO and release the sulfur. This permits a reasonable grade of matte to be obtained. The sulfur not needed to form the matte was vaporized. Some sulfur reacted with the volatile matter of the fuel to form H ,S, COS and other sulfur compounds in which the sulfur is less oxidized than in S0,. These can easily be reacted with SO by conventional means to produce elemental sulfur. The SO can come either from burning a part of these gases or from the converter where the matte sulfur is oxidized. Converter gases may also be used as part of the air blast. The practice of submerged smelting of copper concentrates to volatilize sulfur in a form less oxidized than 50 is shown in FIG. 4. In the practice of this embodiment of my invention. the door was sealed and the gas from exit 12 was treated for elemental sulfur recovery.

What is claimed is:

l. A process for smelting a mineral product in a fur nace. said product being selected from the group con sisting of a concentrate, a rich ore and a calcine, and containing as its major metal constituent copper, zinc or a mixture thereof, said process comprising the steps: preparing a bath of molten slag in a furnace; agitating the bath to maintain a state of turbulence therein by injecting directly into the molten slag finely divided flux and mineral product. an oxygen-bearing gas and optionally a fuel; regulating the amount of fuel, if any, and oxygen-bearing gas injected into the agitated molten slag to control oxidation-reduction reactions and to vaporize at least one component of the mineral product, the amount of oxygen-bearing gas being limited so that any copper matte present in the bath is not oxidized beyond Cu S; and recovering the vaporized component.

2. A process for smelting a mineral product in a furnace, said product being selected from the group consisting of a concentrate, a rich ore and a calcine, and containing as its major metal constituent copper, zinc or a mixture thereof, said process comprising the steps: preparing a bath of molten slag in a furnace; agitating the bath to maintain a state of turbulence therein by injecting directly into the molten slag fuel, a finely divided flux and mineral product and an oxygen-bearing gas; regulating the amount of fuel and oxygen-bearing gas injected into the agitated molten slag to control oxidation-reduction reactions and to vaporize at least one component of the mineral product, the amount of oxygen-bearing gas being limited so that any copper matte present in the bath is not oxidized beyond 01 8; and recovering the vaporized component.

3. The process of claim 2, wherein the fuel is a pulverized solid.

4. The process of claim 2, wherein the fuel is a pulverized coal.

5. The process of claim 2, wherein the component vaporized is selected from the group consisting of zinc, lead, sulfur and sulfur compounds.

6. The process of claim 2, wherein the flux is selected from the group consisting of lime flux, siliceous flux and mixtures of lime and siliceous fluxes.

7. The method of claim 2, wherein the mineral product includes copper as a constituent. said bath being agitated while limiting the amount of oxygen-bearing gas to prevent formation of metallic copper; and removing a copper sulfide matte as molten droplets suspended within the molten slag.

8. The process of claim 7, wherein precious metals within the mineral product are collected by the copper sulfide matte.

9. The process of claim 7, wherein the mineral product is a copper sulfide concentrate, the copper constituent being removed as a matte suspended as molten droplets within the molten slag. the rest of the sulfur component being vaporized largely as sulfur dioxide.

10. The process of claim 9, wherein minor amounts of other metals are also vaporized with the sulfur dioxide to obtain a matte in which the ratio of copper to such other metals is higher than it is in the mineral product treated.

11. The process of claim 7, wherein flux is added to produce slag having sufficient fluidity at l200C. for the matte to settle.

12. The process of claim 7, wherein the mineral product is a copper-iron sulfide from which the copper constituent is recovered as a matte and the remaining sulfur is vaporized largely as forms of sulfur less oxidized 15. The process of claim 14, wherein the mineral is mainly Zinc oxide and the volatilized component is zinc.

16. The process of claim 2, wherein the mineral product contains copper and zinc constituents. the zinc being vaporized and the copper being present in a copper sulfide matte suspended as molten droplets within the molten slag, and thereafter separating the matte from the slag outside the furnace. 

1. A PROCESS FOR SMELTING A MINERAL PRODUCT IN A FURNACE, SAID PRODUCT BEING SELECTED FROM THE GROUP CONSISTING OF A CONCENTRATE, A RICH ORE AND A CALCINE, AND CONTAINING AS ITS MAJOR METAL CONSTITUENT COPPER, ZINC OR A MIXTURE THEREOF, SAID PROCESS COMPRISING THE STEPS: PREPARING A BATH OF MOLTEN SLAG IN A FURNANCE, AGITATING THE BATH TO MAINTAIN A STATE OF TURBULENCE THEREIN BY INJECTING DIRECTLY INTO THE MOLTEN SLAG FINELY DIVIDED FLUX AND MINERAL PRODUCT, AN OXYGEN-BEARING GAS AND OPTIONALLY A FUEL, REGULATING THE AMOUNT OF FUEL, IF ANY, AND OXYGEN-BEARING GAS INJECTED INTO THE AGITATED MOLTEN SLAT TO CONTROL OXIDATION-REDUCTION REACTIONS AND TO VAPORIZE AT LEAST ONE COMPONENT OF THE MINERAL PRODUCT, THE AMOUNT OF OXYGENBEARING GAS BEING LIMITED SO THAT ANY COPPER MATTE PRESENT IN THE BATH IS NOT OXIDIZED BEYOND CU2S, AND RECOVERING THE VAPORIZED COMPONENT.
 2. A process for smelting a mineral product in a furnace, said product being selected from the group consisting of a concentrate, a rich ore and a calcine, and containing as its major metal constituent copper, zinc or a mixture thereof, said process comprising the steps: preparing a bath of molten slag in a furnace; agitating the bath to maintain a state of turbulence therein by injecting directly into the molten slag fuel, a finely divided flux and mineral product and an oxygen-bearing gas; regulating the amount of fuel and oxygen-bearing gas injected into the agitated molten slag to control oxidation-reduction reactions and to vaporize at least one component of the mineral product, the amount of oxygen-bearing gas being limited so that any copper matte present in the bath is not oxidized beyond Cu2S; and recovering the vaporized component.
 3. The process of claiM 2, wherein the fuel is a pulverized solid.
 4. The process of claim 2, wherein the fuel is a pulverized coal.
 5. The process of claim 2, wherein the component vaporized is selected from the group consisting of zinc, lead, sulfur and sulfur compounds.
 6. The process of claim 2, wherein the flux is selected from the group consisting of lime flux, siliceous flux and mixtures of lime and siliceous fluxes.
 7. The method of claim 2, wherein the mineral product includes copper as a constituent, said bath being agitated while limiting the amount of oxygen-bearing gas to prevent formation of metallic copper; and removing a copper sulfide matte as molten droplets suspended within the molten slag.
 8. The process of claim 7, wherein precious metals within the mineral product are collected by the copper sulfide matte.
 9. The process of claim 7, wherein the mineral product is a copper sulfide concentrate, the copper constituent being removed as a matte suspended as molten droplets within the molten slag, the rest of the sulfur component being vaporized largely as sulfur dioxide.
 10. The process of claim 9, wherein minor amounts of other metals are also vaporized with the sulfur dioxide to obtain a matte in which the ratio of copper to such other metals is higher than it is in the mineral product treated.
 11. The process of claim 7, wherein flux is added to produce slag having sufficient fluidity at 1200*C. for the matte to settle.
 12. The process of claim 7, wherein the mineral product is a copper-iron sulfide from which the copper constituent is recovered as a matte and the remaining sulfur is vaporized largely as forms of sulfur less oxidized than sulfur dioxide to facilitate recovering sulfur therefrom.
 13. The process of claim 12, wherein the oxygen-bearing gas also contains sulfur dioxide.
 14. The method of claim 2, said bath of molten slag being enclosed to prevent oxidation of the vaporized component as it is emitted from the bath, the amount of fuel and the oxygen-bearing gas being regulated to vaporize one component in elemental form and produce a reducing gas.
 15. The process of claim 14, wherein the mineral is mainly zinc oxide and the volatilized component is zinc.
 16. The process of claim 2, wherein the mineral product contains copper and zinc constituents, the zinc being vaporized and the copper being present in a copper sulfide matte suspended as molten droplets within the molten slag, and thereafter separating the matte from the slag outside the furnace. 